The present invention relates to a printing control method for controlling an enable signal of a line memory so as to allow reciprocative printing in a video printer.
A video printer is to print a picture recorded by the instant capture of a video signal, or a picture recorded by a recorder such as a still camera and reproduced on a monitor.
Referring to FIG. 1, video decoder 10 of a video color printer separates the R, G, and B analog signals from a video signal input from video input port 5, and the horizontal and vertical synchronous H-sync and V-sync signals. Upon receiving a memory instruction signal from memory instruction input port 15, memory controller 70 supplies a sampling pulse to analog-to-digital converter 20 corresponding to the separated H-sync and V-sync signals. Analog-to-digital converter 20 converts the R, G, and B analog signals from decoder 10 to R, G, and B digital signals corresponding to the sampling pulse from memory controller 70. Frame memory 30 stores the R, G, and B signals from analog-to-digital converter 20 in a storage location corresponding to a write address designated by memory controller 70. Upon receiving an instruction input signal from print instruction input port 25, a printing controller 80 simultaneously applies a read address to frame memory 30, designates a write address in line memory 31, and selects a memory selection switch.
Meanwhile, R, G, and B signals should be converted to yellow Y, cyan C and magenta M in order to be printed on paper. The R, G, and B signals recorded in frame memory 30 are sequentially recorded in line memory 31 by lines by memory selection switch 40, and the data recorded in line memory 31 is transmitted to controller 50 by printing controller 80. Controller 50 converts the R, G, and B signals from line memory 31 to Y, M, and C signals sequentially and at the same time, performs color correction and resistance correction to reduce the resistive deviation of each heat generating element of a printing head in order to compensate the error of density conversion in accordance with the correlation between the properties of the paper used and amount of heat generated by a head, then, applies the converted and compensated Y, M, and C data to the printing head of printing portion 60 in the sequence of Y, M, and C. The data is printed by lines by the printing head of printing portion 60, which is the completion of one frame printing.
Digital-to-analog converter 21 converts the R, G, and B digital signals of frame memory 30 to R, G, and B analog signals and supplies them to encoder 90. Encoder 90 converts the R, G, and B signals converted by digital-to-analog converter 21 to a composite video signal and supplies it to monitor 100. While the one frame picture is being printed by the printing portion, monitor 100 displays the picture which is being printed.
In addition, a printing head of printing portion 60 prints by lines from left to right because the number of vertical sampling is constant but the number of horizontal sampling is variable. Thus, line memory 31 stores one column data during reading out of one frame data from frame memory 30. At this time, printing controller 60 should generate a write enabling signal in order that line memory 31 stores the one column data among one frame data of frame memory 30.
Referring to FIG. 2, frequency divider 110 divides by two a vertical synchronous signal input via vertical synchronous signal input port 105 and supplies the two-divided vertical synchronous signal to up-counter 120. Whenever the vertical synchronous signal divided by two by frequency divider 110 is input to a clock port CLK, up-counter 120 counts a value by increasing it by "1", and supplies the counted value to the input port D of down-counter 130. Down-counter 130 inputs the counted value from up-counter 120 during the horizontal blanking period of a horizontal synchronous signal input via a horizontal synchronous signal input port 115. Whenever a clock signal is applied via clock port 125 during the horizontal scan period of a horizontal synchronous signal, down-counter 130 counts the input values by decreasing it by "1" until the input value becomes "0", and applies a write enabling signal in a predetermined logic state to line memory 31.
Therefore, when the output of up-counter 120 is "1", data (1, L1), (2, L1), (3, L1), . . . , (525, L1) of first column in FIG. 3 is applied and printed in printing portion 7. When the output of up-counter 120 is "2", data (1, L2), (2, L2), (3, L2), . . . , (525, L2) of second column is printed in printing portion 7. According to the sequence, as data (1, L600), (2, L600), (3, L600), . . . , (525, L600) of 600th column is printed, printing of one color is completed.
As printing of one color is completed, a platen drum is rotated two times faster to make paper return to the initial position. Then, printing is carried out again to sequentially print yellow, magenta, and cyan in the same direction, then printing is completed.
As described above, after the completion of printing, the ordinary printing controller rotates the platen drum two times faster to make paper return to the initial position. Then, printing begins again. If paper is wound on the drum, the one-direction printing may cause dislocation of color because of paper's curl and incorrect initial setting.